1rta

Active Site
Ribonuclease A cleaves RNA strands by catalyzing a transphosphorylation reaction where the 2'-OH of the ribose sugar attacks the neighboring phosphate, releasing the ribose on the the other side of the phosphate. This structure shows ribonuclease A (in blue) bound to short DNA strand composed of four thymidines (in pink). Ribonuclease binds tightly to DNA, but since DNA is missing the 2'-OH, ribonuclease does not cleave it. Three amino acids are shown that are important for catalysis. The 3' carbon on the DNA is shown in red--it is the site where the 2'-OH is connected in RNA. The two histidines perform the proton transfers that are needed in the reaction, and the lysine stabilizes the intermediate that is formed as the 2'-OH attacks the phosphate. Ribonuclease cleaves RNA strands best next to cytidine and uridine nucleotides--the reason for this may be seen in a spacefilling representation. Notice that the small pyrimidine base is surrounded by protein atoms. A larger purine base would not fit well in this space.

This section complements the article on Ribonuclease A in the Molecule of the Month Series. See also Teaching Scenes, Tutorials, and Educators' Pages.

About this Structure
1RTA is a Single protein structure of sequence from Bos taurus. The September 2008 Molecule of the Month feature on Ribonuclease A by David Goodsell is http://dx.doi.org/10.2210/rcsb_pdb/mom_2008_9. Full crystallographic information is available from OCA.

Reference
Crystal structure disposition of thymidylic acid tetramer in complex with ribonuclease A., Birdsall DL, McPherson A, J Biol Chem. 1992 Nov 5;267(31):22230-6. PMID:1429575

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